Thermionic valve circuits



Patented pr. 24, 1951 UNITED STATES PATENT OFFICE Application July 21, 1947, Serial No. 762,374 In Great Britain September 1, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires September 1, 1964 (Cl. Z50-27) 16 Claims.

The present invention relates to circuit arrangements employing electron discharge devices, more particularly thermionic valves.

It is knownthat if a condenser is connected between the anode and control grid of a thermionic valve and a 'positive potential is applied to the control grid, a linear fall in the anode voltage occurs until the anode voltage reaches substantially that of the cathode. In my co-pending United States application Serial No. 762,375, led July 21, 1947, entitled Electron Relay Circuit Arrangements, a circuit of this nature is described in which a pent-ode valve is employed and a series of triggering pulses are applied to the suppressor grid to provide repeated operation of the circuit to enable it to be employed, for instance, as a frequency divider, time-base generator or time delay device.

rlhe invention is also concerned with a circuit arrangement in which a condenser is connected between the anode and control grid of a thermionic valve and one of the objects of the invention is to provide such a circuit arangement in which the anode voltage of the valve is reduced in steps in response to voltage changes taking place in the circuit, for instance, due to a series of pulses applied thereto.

According to the invention, in order to enable the step-by-step reduction of anode voltage to take place, a condenser is connected between the anode and control grid of the valve and means are provided which in response to each impulse cause a predetermined charge to be Withdrawn from said condenser thereby causing a sudden fall in the anode voltage of said valve.

According to a feature of the invention in order to enable the step-by-step reduction in the anode voltage to take place in response to a series of impulses applied to the circuit, a condenser is connected between the anode and the control grid of the valve and means are provided which on one edge of a pulse serve to withdraw charge from said condenser through a uni-lateral impedance thereby causing a sudden fall in anode voltage while on the other edge of the pulse said means are restored to their initial condition to enable repeated operation to occur until the anode voltage is reduced substantially to that of the cathode.

A circuit of this nature has numerous applications particularly for counting a predetermined number of pulses and for this purpose, according to a further feature of the invention, means are provided which in response to a series of pulses cause a reduction in the anode voltage of a thermionic valve in equal steps due to the connection of a condenser between the anode and control grid of said valve, the arrangement being such that the anode voltage is reduced substantially to the value of the cathode voltage after the reception of a predetermined number of irnpulses whereupon the anode voltage is returned to its initial value.

According to a further feature of the invention successive pulses are arranged to cause a reduction in the anode voltage of a thermionic valve in equal steps from an initial value to the value of the cathode voltage, the anode voltage then reverting to the initial value and means are provided for varying the extent to each reduction in anode voltage whereby for a given initial value of said voltage the arrangement is able to count different predetermined numbers of pulses.

The invention will be better understood from the following description of one embodiment, given by way of example, taken in conjunction with the accompanying drawings in which Fig. l shows the circuit of the embodiment and Fig. 2 shows the waveforms developed at the electrodes of the various valves shown in Fig. l.

While component values have been added to the circuit shown in Fig. l, it will be understood that they are given solely by way of example to facilitate an understanding of the operation of the circuit and that the invention is in no Way limited thereto.

Referring first to Fig. 1, at some time before the start of a cycle, a square wave is applied to the control grid of V2 in such sense that this valve is cut-ofi. The anode voltage thus rises towards the value of the H. T. supply with a time constant given by R1 (Cl -i-capacity strays from anode to ground). The condenser C! and the stray capacities are thus charged. At this time the control grid of VI is held at a selected positive potential, say at +40 volts, owing to the diode D2, and the cathode, which follows the control grid due to R5 is slightly above this value. rihe suppressor grid of Vl is connected to a source of positive potential, say +25 volts, so that this valve is cut-off on the suppresor grid, the space current passing to the screen grid. The anode voltage thus rises towards 300 volts, the value of the H. T. supply, but is held at some lower value, e. g. 200 volts by the diode DI. The anode of D3 is slightly positive with respect to the cathode so that the condenser Cl is charged to a voltage between that of the anode of D3 and the H. T. voltage.

When the positive-going half of the square vvoltage of V2 also falls to, say, 10 volts.

voltage. of Vl falls.

I `wave is applied to the control grid of V2, the valve conducts and there is a sudden fall in the screen voltage. This sudden fall is applied through the short time-constant diderentiating circuit C336 to the cathode of Di. The anode of Di follows the cathodel and hence the anode voltage of the valve Vl falls followed by its control grid due to the feedback condenser C2. The cathode of V l due to the resistance R5 follows the control grid below the suppressor grid level and the valve Vl is thus triggered, as regards anode current. The anode, control grid and cathode voltages thus fall by, for example 40 volts. The steady fall of anode voltage, which was associated with the circuit disclosed in said United States application Serial No. 762,375 (which is my copending application filed on even date herewith) does not, however, take place in this instance, since there is no leali resistance between the control grid of Vi and the H. T. supply. The anode voltage of Vl thus remains steady and the diode Dl is thus insensitive to further pulses as its anode is 40 volts below the voltage of the cathode. Simultaneously with the fall in voltage of the Ascreen grid of V2 in response to the positivegoing wave applied to the control grid, the anode This fall in anode voltage is transferred to the anode of D3 through the condenser CI until it reaches 1G volts at which value it is maintained by the diode D4. The resulting current flow through the diode De reduces the charge on Cl until it corresponds to a potential difference of 20-volts.

The circuit remains in this condition until the valve V2 is again cut oif by the negative-going 'i portion of the waveform applied to the control grid. The screen grid voltage rises but is without effect and the anode voltage alsoA rises. This -rise is transferred through CI to the anode of trol grid of VI will thus tend to rise but owing to the feedback action from the anode, the control grid voltage is held steady and the anode When CI is fully charged, the current through D3 again ceases and the anode voltage of Vl remains steady. Hence coincident with the rise in the anode voltage of VE, a downward step is produced in the anode voltage of VI. When V2 again conducts, the anode voltage of D3 falls without any corresponding step-.fl

in the anode voltage of VI since D3 does not conduct and Cl is again discharged to about 20 volts potential difference by the action of the diode Dd.

The process is repeated for each input pulse so that the anode voltage of Vl falls one step for each pulse and this continues until the anode voltage approaches that of the cathode. The feedback action then ceases and the next rise in the anode voltage of V2 causes Cl to charge but through the capacity strays from the control grid and anode of V I to earth, Cl taking its charge not from C2 but from the H. T. supply. A sharp rise in anode and control grid voltage of VI occurs followed by a rise in the cathode voltage. The cathode rises to a voltage greater than the +25 volts at which the suppressor grid is maintained, so that Vl is cut-off as regards anode current and the anode voltage rises towards the H. T. voltage with the time constant B2 (C2-lcapacity strays from anode to earth) and is maintained at 200 volts by the diode Di. The circuit is retriggered by the next positive-going edge of the waveform applied to the control grid of V2 which causes a negative pulse to be developed on the screen of V2 and the cycle is repeated. With the values lshown in Fig. 1, the circuit is arranged to count ve impulses and the positive-going edge of the first pulse Serves to trigger the circuit while the negative-going edge of the last pulse serves to return the anode voltage of Vl to its initial value of 200.

The depth of the anode voltage step (relative to the grid potential) is given by C'l C2 (30D-20) y olts since the potential difference across C! varies from 20 to 390 for each step. Since this is fixed and occurs once for each input pulse and the total fall in anode voltage is defined by the potential diierence between the cathode of DI and the cathode of D2, the number of steps between triggering and the return of the circuit toits initial condition, or flash-back will be independent of input frequency provided Cl can charge fully through Rl during the time V2 is cut-off and provided the ash back is complete before V2 is rendered conducting by the next positive-going edge of the applied waveform. The charge time of Cl can be reduced if desired by adding a diode D5 as shown dotted in Fig. l to limit the rise of the anode voltage of V2 to 200 volts.

From the above it will be seen that the number of steps and hence' the number of pulses counted can be adjusted by varying (1) The ratio of Cl to C2 (2) The cathode potential of DI or (3) The cathode potential of D5 or the H. T. potential to which Rl is returned if D5 is not ernployed.

With division ratios up to 10 the circuit is substantially independent of normal valve-to-valve characteristic variations.

It will be noted that the triggering pulses (negative-going pulses applied to the cathode of DI) occur between two step-producing pulses (positive-going edges at the anode of V2). This is because the two sets of pulses are obtained respectively from the positive and negative-going edges of the same square waveform. It will be obvious to those skilled in th-e art, however, that the two sets of pulses could be made coincident by the use of suitable delay networks or by using two sets of pulses. This latter arrangement is particularly useful if it is desired to produce a timing pulse which is adjustable in steps. For this purpose triggering is effected by means of recurrent frequency pulses having a much lower frequency than the step-producing pulses. The recurrence frequency pulses will be employed to trigger the timebase circuit of a cathode ray tube and will also be fed to the anode circuit of VI and to the cathode circuit of Dl through a suitable integrating circuit the cathode of DI being now disconnected from the screen of V2. The circuit will be triggered by the negative-goin edges of the recurrence pulses fed to the anode of V! and the anode voltage of V! will be reduced in steps, the number of steps depending on the initial value of the anode voltage as determined by the. cathode voltage of DI. By feeding the positive-going edges 'of the recurrence pulses to the cathode of DI through an integrating circuit having components of suitable value, the cathode potential may be increased one step for each positive-going edge, an increasing step in the cathode voltage of DI being equal to a decreasing step in the anode voltage of Vl so that succeeding cycles of operation will include one additional decreasing step of anode voltage and the iiashback will occur later in each cycle. The nashback may be used to trigger the circuit of the timing pulse which is applied to the cathode ray tube as brilliance modulation or as a deflection of the timebase trace. Triggering of the circuit of the timing pulse may be effected for instance from the cathode of VI. It will, of course, be understood that the duration of a complete cycle of the circuit will be less than the negative portion of the recurrence pulse applied to the anode of Vl.

It will be appreciated that the circuit will count irregularly spaced negative pulses applied to the control grid of V2 instead of the regular square wave. Alternatively it will count the negative half cycles of a large-amplitude sine wave.

In low frequency circuits, the diode D4 can be replaced by a resistance Whose value is several times that of Rl but is small enough to permit complete discharge of Cl during the period when V2 is conducting.

In a further embodiment of the invention a short-circuited delay network is connected across the resistance Rl and resistances are inserted in the cathode lead of D4 and the anode lead of D3. The delay network will produce a positive-pulse each time the anode of V2 is cut off and the waveform at the junction of the cathode of D4 and the anode of D3 is reduced to a mean Value of -l0 volts due to the added resistance, the anode voltage of D4 being 20 volts in this case. The operation of this circuit is thenceforth the same as that described above.

I claim:

1. An electronic circuit comprising a thermionic valve having at least a cathode, an anode adapted to collect electrons from said cathode, and located between said cathode and anode in the following order a control grid and a further grid; a condenser connected between said control grid and said anode; a feedback resistance in the cathode circuit of said valve; a connection from said further grid to a potential suiiicient to normally prevent electron now from said cathode reaching the anode; a source of voltage pulses; and a unilaterally conducting device connecting said source of pulses to said condenser to thereby vary the charge on the latter.

2. An electronic circuit comprising a thermionic valve having a cathode, an anode adapted to collect electrons from said cathode, and a control grid located between said cathode and said anode; a feedback resistance in the cathode circuit of said valve; a condenser connected between said anode and said control grid; a rst unilaterally conducting device having its cathode connected to the control grid of said thermionic valve; a second unilaterally conducting device having its anode connecting to the anode of said therrnionic valve; a source of voltage pulses; means -for applying pulses from said source to the anode of said first unilaterally conducting device; and means for applying pulses from said source to the cathode of said second unilaterally conducting device.

3. An electronic circuit comprising a thermionic valve having at least, a cathode, an anode adapted to collect electrons from said cathode, and located between said cathode and anode in the following order a control grid, a screen grid, and a further grid; a condenser connected between said control grid and said anode; a direct current voltage source; a resistance connecting said cathode to the negative terminal of said source; a connection from said anode to the positive terminal of said source; a connection from said screen grid to the positive terminal of said source; a connection from said control grid to a potential between that of the positive and negative terminals of said source of direct current voltage; a connection from said further grid to a potential between that to which said control grid is connected and that of the negative terminal of said source; a source of voltage pulses; and a unilaterally conducting device connecting said source of pulses to said condenser so as to vary the charge thereof.

4. An electronic circuit comprising a thermionic valve having at least a cathode, an anode adapted to coliect electrons from said cathode, and located between said cathode and anode in the following order a control grid, a screen grid, and a further grid; a condenser connected between said control grid and said anode; a direct current voltage source; a resistance connecting said cathode to the negative terminal of said source; a first connection from said anode to the positive terminal of said source; a second connection from said control grid to a potential between that of the positive and negative terminals of said source of direct current voltage; a third connection from said further grid to a potential between that to which said control grid. is connected and that of the negative terminal of said source; a fourth connection from said screen grid to the positive terminal of said source; a first unilaterally conducting device having its cathode connected to the control grid of said thermionic valve; a second unilaterally conducting device having its anode connected to the anode of said thermionic valve; means constituting a source of voltage pulses; and means for applying pulses from said source to the anode of said first unilaterally conducting device, said last-named means including means for applying pulses from said source to the cathode of said second unilaterally conducting device.

5. The circuit of claim 4 including in addition means to prevent said control grid from rising above apredeterniined positive potential.

6. The circuit of claim 5 in which said first connection includes high resistance.

'7. The circuit of claim 6 in which the means constituting a source of voltage pulses together with the means for applying pulses from said source to the anode of the rst unilateral conducting device comprise the following elements: a second valve having a cathode, control grid, screen grid and anode; a connection between the cathode of the second valve and the negative side of said source; a resistor connected between the anode of the second valve and the positive side of said source; a condenser connecting the anode of the second valve to the anode of said ilrst unilateral conducting device; means for preventing the anode of said iirst unilateral conducting device from falling below a predetermined negative vaive which value is below that of the negative side of said source; a resistor connecting said lastmamed screen grid to the positive side of said source; a pole of potential which is positive with respect to the negative pole of said source and with respect to the first-named control grid and negative with respect to the positive side of said source; a resistor connecte ing said pole to the cathode of said second unilateral conducting device; and a condenser connected between the last-mentioned cathode and the last-mentioned screen grid.

8. In a frequency dividing circuit; an electron discharge device having a cathode, rst and second grids, and an anode; a direct current source of power having positive and negative sides thereof; a feedback resistor connected between said cathode and said negative side of said source and of such resistance value as to cause said first-named electrode of said device to assume and substantially follow the potential of the second-named electrode thereof; a feedback condenser connected between said anode and said first grid; means for applying a positive potential to said second grid which is lower than the normal potential of the first grid; a second electron discharge device having a cathode, a control grid and first and second electron receiving elements; means for applying the current whose frequency is to be divided between the last-mentioned cathode and said control grid; means connecting the rst-named anode to the positive side of said source and including means connected to one of said electron receiving elements for substantially reducing the anode potential of said rst anode in response to a rst controlling energization of the last-mentioned electron receivingelement; said last-named means including means to cease its effect on the potential of said anode after that potential drops a predetermined amount which is approximately equal to the drop effected by said first controlling energization; and means operated by energization of the other of said electron receiving elements to successively discharge said condenser predetermined amounts for each successive controlling energization until the anode potential of the rst device falls so low that it causes said first grid to restore the circuit to its original condition.

9. In a frequency dividing circuit; an electron discharge device having a cathode, a control grid, a further grid, and an anode; a source of direct current power for the cathode-anode path of said device; a feedback resistor connecting said cathode to the negative side of said source; said resistor being of such resistance value as to cause said cathode to assume and follow the potential of said control grid; means placing a potential on said further grid lower than the quiescent potential of said control grid to thereby oppose anode current flow during quiescent conditions; means connecting said anode to the positive side of said source comprising means operable on receipt of a pulse of the series to be divided to reduce the anode potential to a given value of potential, said last-named means including means to render the same inoperative to further reduce the anode potential until said anode potential again assumes a potential above said given value; a condenser connected between said anode and said control grid for causing the control grid potential to fall when the anode potentialfalls; and means to reduce the charge on said condenser until the control grid effects reversion of the circuit to quiescent condition, said last-named means including means responsive to the pulses to be divided for reducing the charge on said condenser an incremental amount in response to each incoming pulse.

V10. In a pulse-responsive circuit, an electron discharge device having a cathode, first and second grids, and an anode disposed to receive elec- 8, trons from said cathode; a source of direct cuirent for energizing the cathode-anode path of said device; a feedback resistor between said cathode and the negative side of said source; another resistor between said anode and the positive side of said source; a feedback condenser connected between said anode and said rst grid to cause the potential of the rst grid to follow that of the anode; a rectifier having its anode connected to said first-named anode; means connecting the cathode of said rectifier to a second positive potential of less magnitude than that of said positive side; said last-named means including means to reduce the positive potential applied to the last-named cathode in response to each pulse of the series to which the circuit isY intended to respond; means energized by each such pulse for reducing the charge on said condenser in response to each such pulse; and means for applying a sufficient potential to said second grid to oppose passage of current to said anode when the circuit is in the condition at which said condenser is charged to the highest state of charge that it attains.

l1. A circuit for repeating an operation at a slower rate than its control potential repeats comprising an electron discharge device having a cathode, rst and second grids, and an anode; a feedback resistor in series with the cathode to cause the latter to follow potential changes of the first grid; a feedback condenser connected between said anode and control grid to cause the potential of the first grid to follow the anode potential; means for intermittently reducing the charge on said condenser, once for each repeat operation of the incoming potential, thereby causing the condenser to become so discharged as to cut off the current flow at the anode; and means for applying a xed bias to the second grid which is more negative than the cathode when the first grid is above cut-off potential and less negative than the cathode when the rst grid is below cut-off potential.

l2. The circuit dened in claim 11 including means for reducing the anode potential to a predetermined value in response to the pulse next following each rise of anode potential.

13. A circuit comprising an electron discharge device having a cathode, a control grid, and an anode; a condenser connected between said anode and said control grid; means connected to all of the foregoing elements to effect stable operation of the device when the potential of the charge on said condenser is between predetermined limits and for causing the circuit to recharge the condenser to the upper of said limits whenever it falls below the lower of said limits; and means for discharging said condenser incremental amounts of response to receipt of potentials to which response is desired, said lastnamed means including a rectifier connected between the condenser and the incoming potentials.

14. The device dened in claim 10 including -a screen grid located between said first and second grids, and means applying a high positive potential to said screen grid to thereby take the cathode current now when the anode is cut-off from current flow.

l5. In a pulse-responsive circuit, an electron discharge device having a cathode, a control grid, a screen grid, a further grid, and an anode; a source of cathode-anode potential; means connecting said anode to the positive side of said source; a feedback resistor between said cathode and the negative side of said source: a feedback condenser connected between said anode and said control grid to cause the potential of the latter to drop when the anode potential drops; means applying a positive potential to said screen grid to draw cathode current when the anode current is cut-oir; means for applying a potential to the further grid to cut off anode current when the circuit is in quiescent condition; an input; and a rectifier connecting said condenser to said input to cause input pulses to deenergize said condenser and cause the circuit to pass through a cycle of charge and discharge of the condenser in response to a predetermined number of input pulses.

16. A circuit as defined in claim 11 including in addition a further grid between the rst and REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,412,485 Whiteley Dec. 10, 1946 2,416,158 Coykendali Feb. 18, 1947 2,430,570 Hulst Nov. 11, 1947 2,432,292 Deal Dec. 9, 1947 

